The homogeneous enrichment of the intra-cluster and intra-group gas on large scales, as indicated by the little scatter around very shallow radial profiles in the outskirts, is also strongly connected to the history of the chemical enrichment.
The so-called pre-enrichment scenario implies that the gas enriched within proto-groups and proto-cluster galaxies has been displaced beyond their shallower potential wells by some efficient mechanism at early times (\(z\gtrsim 3\) ) — while stellar feedback alone is not sufficient, many recent state-of-the-art cosmological simulations identify the responsible mechanism with early AGN feedback.
This allows the bulk of the diffuse inter-galactic gas to be pre-enriched and then re-accreted into the assembling galaxy group or cluster. This further supports the idea that a significant fraction of the gas chemical enrichment happens at those early times, as confirmed by the little evolution of the gas metallicity below \(z\sim 2\) , especially on the large scales, found
in observations [1]}, [2]}, [3]} and also in simulation studies [4]}, [5]}, [6]}.
At the group scale, cosmological simulations predict a gas metallicity evolution below \(z\lesssim 1\) –2 that is very similar to the one found, and observed, in more massive clusters.
Consistently with the results discussed above, simulations including AGN feedback find a shallow dependence on redshift, especially when the global metallicity within \(R_{500}\)  or the enrichment level in the outer regions (\(\gtrsim 0.3\times R_{500}\) ) is concerned. [7]} show that the evolution of the metallicity in different radial range is similarly mild at groups scales as well, unless only stellar feedback is included in the simulations. In that case, they note again an effective reduction of the gas iron and oxygen content which is more severe particularly in the group regime. This is interpreted as a more substantial, un-suppressed, star formation activity which efficiently, and preferentially, consumes metal-rich gas. In the galactic-outflow model by [8]} a higher growth rate, with respect to observations, was in fact observed in the simulated groups.
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